Amine Attack on the Carbonyl Ligands of the Protonated Dicyclopentadienyl-Bridged Diruthenium Complex [{(η5-C5H3)2(SiMe2)2}Ru2(CO)4(μ-H)]

Complexes [{(η5-C5H3)2(SiMe2)2}Ru2(CO)4(μ-H)]+ (1H+BF4 -, 1D+TfO-), with a protonated Ru−Ru bond, were prepared by protonation of {(η5-C5H3)2(SiMe2)2}Ru2(CO)4 (1) with HBF4·Et2O or CF3SO3D. The bridging proton in 1H+ is removed only very slowly by amine bases even though it is thermodynamically acidic (pK a AN = 6.5 (±0.2)). This remarkable kinetic inertness of the bridging proton allows amines (NH3, NH2CH3, NH(CH3)2, morpholine, piperidine, pyrrolidine) to react with 1H+ by attacking the CO ligand to give a formamide (HC(O)NR2) and the CO-substituted product {(η5-C5H3)2(SiMe2)2}Ru2(CO)3(NHR2) (2). Thus, protonation of the metal−metal bond in 1H+ promotes reactions of the CO ligand that are not possible in the unprotonated 1. A proposed mechanism for these reactions is supported by kinetic studies of the reaction of 1D+TfO- with morpholine in nitromethane at 20.0 °C, as well as by deuterium-labeling experiments. The molecular structure of {(η5-C5H3)2(SiMe2)2}Ru2(CO)3(NH2CH3) (2f), as determined by an X-ray diffraction investigation, is also presented.